I'm still confused by your explanation. You go from talking about import/link to export/append
Never heard of FDB but this link
https://file.org/extension/fdb suggests some possible source apps including MS Dynamics.
Can you open the FDB file itself using Access?
Can you find a way to open the table in a text editor or a hex editor?
Somehow you need to view the data to solve your issue.
You say the structure looks fine so you must be viewing it somehow.
I don't have any more ideas to assist on what you've described so far.
Perhaps someone else will chip in and assist.